The present invention relates to a method for reducing the tackiness of certain soft acrylic polymers. The present invention is particularly useful in relation to ophthalmic lenses made of such soft acrylic polymers, especially foldable intraocular lenses.
Intraocular lenses have been known since about 1950. They are used to replace the natural lenses of eyes which have been damaged by trauma or disease, such as cataracts. A typical intraocular lens (IOL) comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL in the eye. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA), and it may be hard, relatively flexible or even fully deformable in order to permit the IOL to be rolled or folded and inserted through a relatively small incision in the eye. The haptic is generally made of some resilient material, such as polypropylene or PMMA. The IOLs can have either a "one-piece" or a "multi-piece" design. A multipiece lens is so called because the optic and the haptic(s) are made separately and then the haptics are attached to the optic. In a one-piece lens, the optic and haptic(s) are formed out of one piece of material, and depending on the material, the haptics are then cut, or lathed, out of the material to produce the IOL.
European Patent Publication No. 485 197 A1 (published 13 May 1992) discloses a class of soft acrylic polymers which are suitable for forming IOLs which have high refractive index, are flexible and transparent, can be inserted into the eye through a relatively small incision and recover their original shape after insertion. Although this type of lens material is advantageous in that thinner lenses may be crafted, which allow the IOLs to be folded and permit the use of smaller incisions, it has been found that this type of lens material has a tendency to adhere to itself, as well as to the handling tools. In fact, the inserted IOL can take several minutes to release from itself following insertion. A tacky lens requires more manipulations by the surgeon and increases surgery time (because of the manipulations and lengthy unfolding time). The reduced surface tack lens can be more easily manipulated during surgical implantation. The final outcome with a reduced surface tack lens is easier IOL placement, reduced surgery time, and greater safety for the patient.
Both chemically non-reactive and chemically reactive plasmas have been used to treat various polymer surfaces for several years. See, for example: Inagaki et al., "Adhesion of Glow Discharge Polymers to Metals and Polymers," Journal of Applied Polymer Science 26:3333-3341 (1981), and Inagaki et al., "Distribution of Polymer Deposition in Glow Discharge Polymerization in a Capacitively Coupled System," Journal of Applied Polymer Science, 26:3425-3433 (1981). In addition, plasma treatments have recently been used to treat silicone contact lenses and silicone intraocular lenses. See, for example: Ho et al., "Ultrathin Coating of Plasma Polymer of Methane Applied on the Surface of Silicone Contact Lenses," Journal of Biomedical Materials Research, 22:919-937 (1988); Hettlich et al., "Plasma-induced Surface Modifications on Silicone Intraocular Lenses: Chemical Analysis and In Vitro Characterization," Biomaterials, 12:521-524 (1991); and Tidwell, C. D., "The Development of a Surface-modified, Self-passivating Intraocular Lens," Master of Science Thesis, University of Washington (1990).
While plasma treatments have been used to modify other types polymer surfaces, the Applicants are not aware of any prior use of plasma treatments to reduce polymer surface tackiness of soft acrylics.